A
- Afghanistan
- Albania - 1 March 1922
- Algeria - 1 October 1907
- Angola - 1 March 1977
- Antigua and Barbuda - 20 January 1994
- Argentina - 1 April 1878
- Armenia - 14 October 1992
- Aruba, Curaçao and Sint Maarten - 1 July 1875[1]
- Aruba
- Curaçao
- Sint Maarten
- Australia - 1 October 1907
-
- Norfolk Island
- Austria - 1 July 1875
- Azerbaijan - 1 April 1993
B
- Bahamas - 24 April 1974
- Bahrain - 21 December 1973
- Bangladesh - 7 February 1973
- Barbados - 11 November 1967
- Belarus - 13 May 1947
- Belgium - 1 July 1875
- Belize - 1 October 1982
- Benin - 27 April 1961
- Bhutan - 7 March 1969
- Bolivia - 1 April 1886
- Bosnia and Herzegovina - 1 July 1892; 26 January 1993
- Botswana - 12 January 1968
- Brunei - 15 January 1985
- Brazil - 1 July 1877
- Bulgaria - 1 July 1879
- Burkina Faso - 29 March 1963
- Burundi - 6 April 1963
C
- Cambodia - 21 December 1951
- Cameroon - 26 July 1960
- Canada - 1 July 1878
- Cape Verde - 30 September 1976
- Central African Republic - 28 June 1961
- Chad - 23 June 1961
- Chile - 1 April 1881
- China - 1 March 1914
- Republic of China (Taiwan)
- People's Republic of China
- Colombia - 1 July 1881
- Comoros - 29 July 1976
- Congo, Democratic Republic of the - 1 January 1886
- Congo, Republic of - 5 July 1961
- Costa Rica - 1 January 1883
- Côte d'Ivoire (Ivory Coast) - 23 May 1961
- Croatia - 20 July 1992
- Cuba - 4 October 1902
- Cyprus - 23 November 1961
- Czech Republic - 18 May 1920; 18 March 1993
D
- Denmark - 1 July 1875
-
- Faroe Islands
- Greenland
- Djibouti - 6 June 1978
- Dominica - 31 January 1980
- Dominican Republic - 1 October 1880
E
- Ecuador - 1 July 1880
- Egypt - 1 July 1875
- El Salvador - 1 April 1879
- Equatorial Guinea - 24 July 1970
- Eritrea - 19 August 1993
- Estonia - 7 July 1922; 30 April 1992
- Ethiopia - 1 November 1908
F
- Fiji - 18 June 1971
- Finland - 12 February 1918
- Åland
- France - 1 January 1876
- French Overseas Departments
- French Guiana
- Guadeloupe (including Saint Barthélemy and Saint Martin)
- Martinique
- Réunion
- Mayotte
- Saint Pierre and Miquelon
- Territories coming within the UPU's jurisdiction by virtue of article 23 of the UPU Constitution
- French Polynesia (including Clipperton Island)
- French Southern and Antarctic Lands
- New Caledonia
- Wallis and Futuna
G
- Gabon - 17 July 1961
- Gambia - 9 October 1974
- Georgia - 1 April 1993
- Germany - 1 July 1875
- Ghana - 10 October 1957
- Greece - 1 July 1875
- Grenada - 30 January 1978
- Guatemala - 1 August 1881
- Guinea - 6 May 1959
- Guinea-Bissau - 30 May 1974
- Guyana - 22 March 1967
H
I
- Iceland - 15 November 1919
- India - 1 July 1876
- Indonesia - 1 May 1877
- Iran - 1 September 1877
- Iraq - 22 April 1929
- Ireland - 6 September 1923
- Israel - 24 December 1949
- Italy - 1 March 1957
J
- Jamaica - 29 August 1963
- Japan - 1 June 1877
- Jordan - 16 May 1947
K
- Kazakhstan - 27 August 1992
- Kenya - 27 October 1964
- Kiribati - 14 August 1984
- Korean Empire - 1 January 1900
- Korea, Democratic People's Republic of - 6 June 1974
- Korea, Republic of - 15 August 1948
- Kuwait - 16 February 1960
- Kyrgyzstan - 26 January 1993
L
- Laos - 20 May 1952
- Latvia - 1 October 1921; 17 June 1992
- Lebanon - 12 May 1931; 15 May 1946
- Lesotho - 6 September 1967
- Liberia - 1 April 1879
- Libya - 4 June 1952
- Liechtenstein - 13 April 1962
- Lithuania - 1 January 1922; 10 January 1992
- Luxembourg - 1 July 1875
M
- Macedonia - 12 July 1993
- Madagascar - 2 November 1961
- Malawi - 25 October 1966
- Malaysia - 17 January 1958
- Maldives - 15 August 1967
- Mali - 21 April 1961
- Malta - 21 May 1965
- Mauritania - 22 March 1967
- Mauritius - 29 August 1969
- Mexico - 1 April 1879
- Moldova - 16 November 1992
- Monaco - 12 October 1955
- Mongolia - 24 August 1963
- Montenegro - 26 July 2006
- Morocco - 1 October 1920
- Mozambique - 11 October 1978
- Myanmar - 4 October 1949
N
- Namibia - 30 April 1992
- Nauru - 17 April 1969
- Nepal - 11 October 1956
- Netherlands - 1 July 1875
- New Zealand (including the Ross Dependency) - 1 October 1907
-
- Cook Islands
- Niue
- Tokelau
- Nicaragua - 1 May 1882
- Niger - 12 June 1961
- Nigeria - 10 July 1961
- Norway - 1 July 1875
O
- Oman - 17 August 1971
P
- Pakistan - 10 November 1947
- Panama - 11 June 1904
- Papua New Guinea - 4 June 1976
- Paraguay - 1 July 1881
- Peru - 1 April 1879
- Philippines - 1 January 1922
- Poland - 1 May 1919
- Portugal - 1 July 1875
Q
- Qatar - 31 January 1969
R
- Romania - 1 July 1875
- Russia - 1 July 1875
- Rwanda - 6 April 1963
S
- Saint Kitts and Nevis - 11 January 1988
- Saint Lucia - 10 July 1980
- Saint Vincent and the Grenadines - 3 February 1981
- Samoa - 9 August 1989
- San Marino - 1 July 1915
- São Tomé and Príncipe - 22 August 1977
- Saudi Arabia - 1 January 1927
- Senegal - 14 June 1961
- Serbia - 1 July 1875; 24 December 1921; 18 June 2001
- Seychelles - 7 October 1977
- Sierra Leone - 29 January 1962
- Singapore - 8 January 1966
- Slovakia - 18 May 1920; 18 March 1993
- Slovenia - 24 December 1921; 27 August 1992
- Solomon Islands - 4 May 1984
- Somalia - 1 April 1959
- South Africa - 1 January 1893; 22 August 1994
- South Sudan - 4 October 2011
- Spain - 1 July 1875
- Sri Lanka - 13 July 1949
- Sudan - 28 July 1956
- Suriname - 1 May 1877; 20 April 1976
- Swaziland - 7 November 1969
- Sweden - 1 July 1875
- Switzerland - 1 July 1875
- Syria - 12 May 1931; 15 May 1946
T
- Tajikistan - 9 June 1994
- Tanzania - 29 March 1963
- Thailand - 1 July 1885
- Timor-Leste - 28 November 2003
- Togo - 21 March 1962
- Tonga (including Niuafo'ou) - 26 January 1972
- Trinidad and Tobago - 15 June 1963
- Tunisia - 1 July 1888
- Turkey - 1 July 1875
- Turkmenistan - 26 January 1993
- Tuvalu - 3 February 1981
U
- Uganda - 13 February 1964
- Ukraine - 13 May 1947
- United Arab Emirates - 30 March 1973
- United Kingdom - 1 July 1875
- Acceded automatically as Crown dependencies of the United Kingdom
- Guernsey
- Isle of Man
- Jersey
- British overseas territories - 1 April 1877
- Anguilla
- Bermuda
- British Indian Ocean Territory
- British Virgin Islands
- Cayman Islands
- Falkland Islands
- Gibraltar
- Montserrat
- Pitcairn Islands
- South Georgia and the South Sandwich Islands
- Saint Helena, Ascension and Tristan da Cunha
- Dependencies of St Helena
- Ascension
- Tristan da Cunha
- Turks and Caicos Islands
- United States - 1 July 1875
- Territories coming within the UPU's jurisdiction by virtue of article 23 of the UPU Constitution
- Guam
- Puerto Rico
- American Samoa
- United States Virgin Islands
- Northern Mariana Islands
- Uruguay - 1 July 1880
- Uzbekistan - 24 February 1994
V
- Vanuatu - 16 July 1982
- Vatican City - 1 June 1929
- Venezuela - 1 January 1880
- Vietnam - 20 October 1951
Y
- Yemen - 1 January 1930
Z
- Zambia - 22 March 1967
- Zimbabwe - 31 July 1981